The construction of thin concrete walled structures such as hyperbolic cooling towers requires that the walls forming the structure be poured as a continuous unit. This is accomplished by forming one level or lift to be poured and pouring that level around the entire circumference of the structure. Thereafter, the forms are moved upwardly for the next lift which is poured as a continuous or integral part of the lower lift and so on until the entire height of the structure has been poured.
There are many different ways in practice for forming the repeated lifts necessary to pour an entire structure. In one method, scaffolding is built upon the ground and each successive lift requires additional scaffolding and forming, all of which is supported upon the lower levels of scaffolding for the entire height of the structure. In another method, no ground engaging scaffolding is employed but, instead, the concrete wall of the lift below is utilized as the supporting medium for apparatus extending above which secures the form for the next lift in place. It is this latter self-supporting forming apparatus to which the improvements of the present invention apply.
In the self-supporting type forming apparatus, a plurality of jacking beams are secured through anchor bolts, to the lower and most recently poured lift around the entire outer circumference of the structure. The upper portion of the I beam extends above the lift poured below. A pair of moving beams spaced on the outer flange of the jacking beam operating through a jack and ratchet arrangement permit the moving beams to jack the apparatus upwardly on dogs along the jacking beam until the height of the next desired lift or pour is reached. At that point, forming material is positioned between adjacent jacking apparatus and held in place against the inner surface of the inner flange of the jacking beam by a compression beam carried by the moving beams. A similar plurality of form positioning apparatus and associated jacking beams are positioned around the entire inner circumference of the structure to provide the required form cavity for the lift to be poured.
After all forms are in place, both on the inside and outside circumference of the structure, the lift will be poured as a continuous lift around the entire circumference. While this is being done, additional anchor bolts are placed in the pour between adjacent form pouring apparatus. After the concrete is set and the forms removed, these anchor bolts will be used to position a further set of I beams which will extend above the top of the pour a distance equal to the next pour to be made. These I beams will match at their lower ends with similar I beams anchored into the lift below and upon which are positioned identical form pouring apparatus used for that lift. The lower set of form pouring apparatus will then be jacked upwardly from one beam onto the next until it has reached the level of the next pour. In this way, alternate sets of form pouring apparatus are utilized to pour the entire structure.
In the self-supported form positioning apparatus currently in use, the force to maintain the form in place was created by means of a wedge driven between the compression beam and the structure associated with the moving beam. The wedges have a tendency to work loose and permit the form to be released. Additionally, a very real hazard existed in removing the wedges. Quite often, they will become dislodged and fall from the structure creating a hazard to workers below the forms.
The form positioning apparatus of the type in use additionally employs structure associated with the moving beams to deflect the jacking beam either inwardly or outwardly. In such devices as a hyperbolic cooling tower, the forms must be slightly curved in each lift to provide the overall curvature of the structure through the many lifts required to pour the structure.
In one mode of beam deflection in the apparatus currently in use, the top rollers on the lower ends of the moving beams are forced downwardly against the outer edges of the outer flange of the jacking beam. This condition results in great stress being placed on the outer edges of the outer flange with consequent bending or cracking of the flanges. The jacking beams are usually made of aluminum and are very costly to replace.